Apparatus for indicating differences in pressure



June 5, 1962 K. T. KALLE 3, 3

APPARATUS FOR INDICATING DIFFERENCES IN PRESSURE F'i led Oct. 27. 1958 KHI T. KALLE INVENTOR' VJDW LJ-WMMVZ United States Patent Ofiice Patented June 5, 1962 3,037,389 APPARATUS FOR INDICATING DIFFERENCES IN PRESSURE Karl Torsten Kalle, Sandbacken, Sallie, Sweden Filed Oct. 27, 1958, Ser. No. 769,993 Claims priority, application Sweden Nov. 20, 1957 Claims. (Cl. 73-401) The present invention relates to an apparatus capable of indicating even very small differences between different gas pressures, e.g. a minor deviation in either direction between a certain gas pressure and the atmospheric pressure prevailing at the moment. As a specific example of the use of the apparatus, there may be mentioned the control of the sub-pressure in a furnace where it is desired to maintain as low as possible a difference in pressure with respect to the surrounding atmosphere, without any risk of smoke being driven back into the stokehold.

According to the invention, the apparatus comprises two communicating containers for holding liquid and adapted to be connected above the liquid levels to sources of gas, the pressures of which are to be compared, means for maintaining a constant liquid level in one container, a smaller vessel located in the second container and provided with an inlet, the smaller vessel being suspended in a bourdon pipe which is flexible in the vertical direction, a pump adapted to be driven at a constant speed and having its suction side connected to the vessel by means of a conduit permitting the vessel to be raised and lowered in dependence upon the bending of the bourdon pipe, a restricted outlet from the pressure side of the pump and conduits from the pressure side to the bourdon pipe as well as to a pressure indicating instrument, wherein the bourdon pipe normally holds the vessel raised in a position where its inlet opening is approximately at the liquid level in the surrounding container, so that the pump vw'thdraws a mixture of gas and liquid, the composition of which determines the pressure arising at the pressure side of the pump and acting upon the bourdon pipe and the indicating instrument.

The device according to the invention is described in more detail with reference to the accompanying drawing, in which the single FIGURE shows a vertical section of a preferred embodiment.

In the drawing, 1 designates a closed container which can be connected to a source of gas by means of a conduit 2. An upright, tubular cylinder 3 provided with a transverse partition 4 is secured in a fixed position within the container 1, with its lower end slightly above the bottom of the container 1. A filter 5 consisting of screening-cloth, wire gauze or the like is inserted in the lower end of the cylinder 3. Another cylinder 6 is threaded on the upper end of the cylinder 3 and forms together with the partition 4 one of the communicating containers mentioned above. A casing 7 containing a rotor 8 with blades 9 is mounted on the partition 4, which forms the bottom wall of the casing 7. A central opening 10 is provided in this wall 4 opposite the rotor 8. The wall of the casing 7 is provided with an outlet passage 11 directed radially in relation to the rotor 8. The container 1 is intended to be half filled with liquid, generally some kind of oil, and in operation the rotor 8 causes liquid to be drawn through the central opening 10 and to be fed through the radial hole 11 which communicates with the lower part of the vessel 6. The vessel 6 is thereby always kept filled with liquid over-flowing its rim and, in this way, a constant liquid level is maintained in the vessel.

A pump housing 12 is mounted above the rotor casing 7. It contains a gear pump, one gear wheel 13 of which is shown in the figure. If desired, the rotor casing 7 and the pump housing 12 may be made integral. The gear wheel 13 shown is secured to the rotor shaft 8, while the gear Wheel not shown in the drawing is mounted on a driving shaft coupled to a motor.

The pump housing 12 supports a cylindrical vessel 14 which extends vertically upwards through the upper wall of the container 1 into a chamber 15 placed on top of the container 1. A conduit 16 is provided to connect the chamber 15 to a gas room or the like in which the pressure is to be controlled. The vessel 14- communicates with the chamber 15 through an axial slot 17 in the upper portion of its wall, and the lower portion of the vessel communicates with the surrounding vessel 6 by means of openings 18 through which liquid enters and rises to a level determined by the difference between the pressures in the container 1 and in the chamber 15. Thus, the vessel 14 forms the second of the two communicating containers mentioned above.

The chamber 15 contains a bourdon pipe 19, one end of which is fixed to the bottom of the chamber 15. A rod 24) secured to the free end of the bourdon pipe 19 extends through the slot 17 into the vessel 14, where it carries a vertical tube 21 having a diameter essentially smaller than that of the vessel 14. The lower end of this tube 21 is slidably mounted with a reasonably good seal over a pipe socket 22 extending upwards from the pump housing 12. A channel through the wall of the pump housing 12 connects the pipe 22 with the suction side of the pump. A pin 23 projects axially from the upper end of the tube 21 and is slidably guided in a corresponding hole in the upper end wall of the surrounding vessel 14. Thus, the tube 21 is movable in the axial direction and, as shown in the drawing, it is preferably loosely suspended on the end of the rod 20 which engages the lower edge of a collar or flange provided around the tube 21. At some distance from its ends, the tube 21 has a side opening, preferably in the form of an axial slot 24. The lower edge of this slot 24 is normally located approximate at the liquid level in the surrounding vessel 14, as described below.'

It is to be noted that the tube '21 described can be conveniently replaced by some other nozzle member, the nozzle of which is held at the liquid level.

A restricted channel 25, extending from the pressure side of the pump through the Wall of the housing 12, is connected to an outlet conduit 26 which has a widened portion 27 directed upwardly and opening into the chamber 15. A discharge pipe 28 branches ofi from the widened tube portion 27 within the container 1. Another conduit 29 from the pressure side of the pump is divided into two branches, one of which, shown at 30, is connected to the fixed end of the bourdon pipe 19, While the other branch, the conduit 31, is connected to a pressure indicating instrument, for instance a manometer 32, which may be designed as a recording instrument, if desired' The device described operates as follows. Initially, when atmospheric pressure prevails in the container 1 as well as in the chamber 15, the liquid level in the vessel 14 is exactly at the same height as the constant level in the vessel 6. The gear pump 13 (which should be driven at a constant speed) is intended to operate with a mixture of gas and liquid in the known way. This mixture is withdrawn from the tube 21 to which liquid is supplied through the slot 24. Owing to the restricted outlet 25, an overpressure is established at the pressure side of the pump and its magnitude depends upon the proportion of liquid in the mixture passing through the pump. If the pump only withdraws gas, the pressure would thus be very low or insignificant. In the embodiment shown, however, the pump always withdraws a certain minimum amount of liquid through an additional inlet 33, so that the proportion of liquid never falls to zero. The degree of bending of the bourdon pipe 19 will, of course, be dependent upon the pressure at the pressure side of the pump and, in the initial position mentioned above, only a comparatively slight overpressure is required to cause the bourdon pipe 19 to hold the suction tube 21 raised to such a height that the proportion of gas supplied to the pump is large enough to maintain this moderate over-pressure. In other words, the tube 21 is raised to such a level that the lower edge of the slot 24 is located at or only slightly below the liquid surface in the vessel 14, so that the pump withdraws almost the maximum amount of gas.

It is assumed that the container 1 is permitted to maintain its communication with the atmosphere through the inlet 2 and that the conduit 16 from the chamber 15 is connected to a furnace in which a slightly lower pressure is maintained. Owing to this lower pressure, the liquid level in the vessel 14 rises correspondingly, so that more liquid is supplied through the slot 24 and the pump withdraws liquid exclusively. The increased pressure at the pressure side of the pump straightens the bourdon pipe 19 a little, whereby the suction pipe 21 is raisd so that a certain proportion of gas is again drawn in and a new equilibrium is established. However, it should be noted that a greater pressure is required to keep the bourdon pipe 19 in this position and therefore the suction pipe 21 must be kept at such a height that the proportion of liquid supplied to the pump is greater than before. In other words, the lower edge of the slot will be held a little deeper below the liquid level in the vessel 14.

The greater pressure on the pressure side of the pump also affects the manometer 32, which is preferably graduated to indicate directly the difference between the pressures in the container 1 and the chamber 15.

The mixture of gas and liquid discharged from the pump rises slowly in the widened tube 27, so that the gas has time to separate from the liquid for the greater part and return to the chamber 15 from where it came initially. In this way, the pump causes no change of the gas pressure in the chamber at its operation. The liquid which is substantially freed from gas flows off through the outlet 28.

The apparatus described is more sensitive as the hourdon pipe is the more rigid. This of course is due to the fact that a more rigid bourdon pipe requires a greater pressure to be straightened and such a greater pressure results in a correspondingly greater angular deflection on the manometer. The sensitivity can readily be made so high that the manometer gives a fully clear indication even when the difference in pressure is 0.1 mm. of water or less, which may be considered as more than sufiicient for the control of a heating furnace, for instance, where the subpressure is generally kept at 2-5 mm. of water.

If the apparatus is designed to operate with great sensitivity, its range of operation will evidently be correspondingly more restricted, i.e. because a manometer only makes a certain angular deflection. In such case, the range of operation may be changed by screwing the cylinder 6 upwards or downwards over the cylinder 3, so that the constant liquid level in the cylinder 6 is raised and lowered respectively. Thus, it is possible to adjust different control ranges for the same apparatus, e.g. 5-0 mm. overpressure, -5 mm. sub-pressure and -10 sub-pressure.

The apparatus according to the invention may be used for indicating small differences in pressure within many different fields. The conduit 2 may of course be connected to a source of pressure, if desired, and it is not absolutely necessary for the lower pressure to act upon the liquid surface in the vessel 14. In some cases, differences in pressure only constitute indirect measures of other quantities, such as temperatures, and then the manometer may be graded to indicate these quantities directly. Further, the apparatus may be used for purposes of regulation, if the manometer conduit 31 is connected to a regulator which performs a desired adjustment in dependence upon the variations in pressure occurring at the pressure side of the pump.

What I claim is:

1. An apparatus for indicating small differences in pressure, comprising a first container, a second container connected to a lower portion of said first container communicating with said first container, said containers containing a liquid and being connected above the liquid levels to sources of gas whose pressures are to be compared, means for maintaining a constant liquid level in said first container, a vertically disposed vessel located in said second container having a first inlet spaced from the bottom thereof and a second inlet below said first inlet, a vertically flexible bourdon pipe supporting said vessel, a pump driven at constant speed, a first conduit connected to said vessel at said second inlet and to the suction side of said pump so that said vessel may be raised and lowered in dependence upon the bending of said bourdon pipe, said pump having a restricted outlet at its pressure side, a second conduit from said pressure side of said pump to said bourdon pipe which normally holds said vessel raised in a position where said first inlet is approximately at the liquid level in said second container so that limited amounts of liquid flow into said vessel and consequently said pump withdraws a mixture of gas and liquid from said vessel, the composition of which determines the pressure arising at the pressure side of said pump and acting upon the bourdon pipe and a pressure indicating instrument connected to said conduit from the pressure side of the pump to indicate the pressure in said conduit.

2. An apparatus according to claim 1 in which the means for maintaining a constant liquid level in said first container comprises a second pump to supply liquid continuously to said first container.

3. An apparatus according to claim 1 in which said first container is adjustable in height.

4. An apparatus for indicating small differences in pressure, comprising a first container, a second container connected to a lower portion of said first container communicating with said first container, a liquid-containing third container enclosing said first container and connected above the liquid level to a first source of gas, means for supplying liquid continuously from said third to said first container which is provided with an overflow, a vertically disposed vessel located in said second container having a first inlet spaced from the bottom thereof and a second inlet below said first inlet, a bourdon pipe flexible in the vertical direction carrying said vessel at its free end, a chamber enclosing said bourdon pipe and the open upper portion of said second container, said chamber being connected to a second source of gas the pressure of which is to be compared with the pressure of said first source of gas, a pump driven at constant speed, a first conduit connected to said vessel at said second inlet and to the suction side of said pump so that said vessel may be raised and lowered in dependence upon the bending of said bourdon pipe, said pump having a restricted outlet at its pressure side, a second conduit from said pressure side of said pump to said bourdon pipe which normally holds said vessel raised in a position where said first inlet is approximately at the liquid level in said second container so that limited amounts of liquid flow 5 6 into said vessel and consequently said pump withdraws the liquid level in said third container to return the a mixture of gas and liquid from said vessel, the com liquid escaping from the pump. position of which determines the pressure arising at the a 5. An apparatus according to claim 4 in which said pressure side of said pump and acting upon the bourdon first container is adjustable in height. pipe, a pressure indicating instrument connected to said 5 conduit from the pressure side of the pump to indicate R f e ce Cited in the file of this patent the pressure in said conduit, a rising tu-be connected to said restricted outlet and ending into said chamber to UNITED STATES PATENTS return the gas escaping from the pump, and a branch 2,598,178 Kane May 271 1952 conduit extending from said rising tube to a point below 10 2599,459 Kane June 1952 

